1. Field of the Invention
The present invention generally relates to card edge connectors, and particularly to high-speed card edge connectors.
2. Description of Related Art
In today's high speed electronic systems, it is desirable that all components of an interconnection path be optimized for signal transmission characteristics, otherwise the integrity of the system will be impaired or degraded. High-speed card edge connectors are popular type of electrical connector that require passing fast rise time signals without distorting or degrading that rise time. Such high-speed card edge connectors are generally employed in computer and telecommunication equipments.
A conventional card edge connector commonly has an elongated housing defining an elongated slot for receiving a mating edge of a daughter printed circuit board or a card. A plurality of terminals are spaced along one or both sides of the slot for engaging contact pads adjacent the mating edge of the daughter printed circuit board to thereby establish electrical interconnection between the daughter card and a mother backplane printed circuit board on which the card edge connector is mounted. Such card edge connectors typically utilize preload features in the contacts in order to achieve a suitable contact force between the contacts and the inserted card.
U.S. Pat. Nos. 5,062,292 and 5,051,099 both disclose typical card edge connectors. Signal contact members of those card edge connectors are loaded from a mounting face of the housing and are inserted so that free tips thereof rest behind a plastic wall that exists between the card and the tips. Outwardly extending flanges of an intermediate portion of each signal contact member engage a corresponding flange receiving surface within the housing to lock the signal contact members within the housing. Noticeably, such a preloaded contact tip requires a long portion of the contact to extend above the contact-card interface. This length is required not only for providing a preload feature but also for allowing a sufficient lead-in portion on the contact. This tip design adds significant capacitance because the tip consists of a long extension that does not lie within the current path. This capacitance is detrimental to signal integrity. In common industry language, this tip design can be described as having a large electrical stub. In addition, the surface pads on the plug-in card are usually enlarged to provide sufficient surface area for the mating of the contacts. The increased surface area at the mating location increases the residual capacitance on the plug-in card, therefore further degrading signal integrity.
U.S. Pat. No. 5,919,049 discloses another conventional card edge connector. Similarly, the connector has preloaded contacts secured in the housing. It can be readily seen that the contacts as disclosed in these prior arts have tips pointing towards the inserted card. Clearly, it adds the risk of the card mechanically stubbing on the sheared tips of the contacts. Moreover, it is not easy to reduce the connector height for such a tip design.
U.S. Pat. No. 6,926,565 discloses another type of high speed card edge connector. The '565 patent suggests a modified geometry of the retention mechanism that holds the contact into the housing. In prior art for lower speed signals, the retention mechanism consists of a solid tab. The solid tab adds a discrete capacitance element between adjacent signal lines. Discrete capacitance elements within a connector's construction will degrade signal transmission. The '565 patent invention makes the solid tab a U shape geometry, forcing the current to flow around the outside perimeter defined by the retention mechanism. This geometry reduces capacitance and adds inductance. This balancing of capacitance and inductance provides better signal transmission. However, the '565 patent simply removes capacitance from a retention mechanism of the contact.
Hence, an improved high-speed card edge connector is highly desired.